Constant velocity joints are typically employed in automotive axial drive shafts, and especially in front-wheel-drive vehicles between the transaxle differential and the driving wheel. They are used to transmit torques at various speeds, angles and telescopic positions between a first shaft and second shaft.
There are many types of CV joints. One CV joint configuration includes a rotatable first shaft that has an axle portion and a pocket end disposed at an end of the axle portion. The first shaft is rotatable about a first longitudinal axis. The pocket end is disposed within a joint housing that is disposed on an end of a second shaft. The second shaft is rotatable about a second longitudinal axis. The joint housing includes a plurality of grooves disposed within a central bore and extending along the second longitudinal axis. The pocket end includes a diameter transverse to the first longitudinal axis that is greater than a diameter of the axle portion of the first shaft. The pocket end defines a plurality of semi-spherical pockets that are circumferentially and radially disposed about the first longitudinal axis in a configuration that is complementary relative to the plurality of grooves. As such, the number of pockets is equal to the number of grooves. The CV joint includes a plurality of spherical drive balls with one drive ball rotatably disposed within each pocket and corresponding groove. The pocket end and first shaft are moveable and may be articulated or stroked axially relative to the second shaft. As the CV joint is articulated (i.e., as the second shaft is moved relative to the first shaft by axial stroking or angulation) the drive balls roll back and forth along the grooves and rotate within the pockets.
The drive balls have a spherical shape. The ball pockets have a semi-spherical shape. The radius of curvature of the pockets is generally larger than the radius of curvature of the drive balls. It is generally desirable to have the ball pockets conform closely to the drive balls, and thus to have the radius of curvature of the ball pockets as close to that of the drive balls as possible. Grease is generally disposed within the pockets, between the pockets and the drive balls, and otherwise disposed within the joints so that it is made available to the drive balls. However, as radius of curvature of the ball pockets becomes close to that of the drive balls, the tight conformance of the balls to the pockets make it difficult to provide lubrication between them causing the interface to become starved of lubricant and leading to high friction and concomitant high wear of one or both of the balls or pockets.
Accordingly, there remains a need to provide stroking CV joints of the types described having improved lubrication and methods of making these joints.